1. Field of the Invention
The present invention relates generally to the field of electro-optical detecting apparatus which utilizes two-dimensional detector arrays to provide surveillance of an extensive scene and more particularly, to a two-dimensional infrared focal imaging plane having high resolution and high efficiency without requiring the use of cooling devices.
2. Prior Art
In thermal imaging systems infrared radiation emitted by objects as well as the infrared emitted from the background of a scene is focused by infrared optics on a focal imaging plane wherein infrared detectors convert such radiation into electrical signals. Such electrical signals can be converted for display on a cathode ray tube to provide a visible image of the infrared image. Because infrared imaging does not depend on illumination of a scene, thermal imaging systems are particularly conductive for many day and night applications.
The most recent prior art is characterized by thermal imaging systems which utilize mechanical scanning optics to produce an infrared image in a focal plane comprising an array of cooled infrared photon detectors. By way of example, this concept is illustrated in U.S. Pat. No. 3,723,642 to Laakmann. In this implementation, a short array of detectors, such as 10-30 detectors, is scanned two-dimensionally across the image. The detectors are oriented parallel to the line scan dimension of the television raster to be generated. The signals from the detectors are summed appropriately in a delay line and processed to provide the image. Another recent prior art development consists of staring systems utilizing cooled or uncooled two-dimensional detector arrays which are electronically readout by a two-dimensional charge coupled device or a cross bar switch array. The detector focal planes of staring systems utilize solder bumps to connect each detector of the array to an appropriate readout node of an integrated circuit on a substrate. Cooled infrared detectors require solder bumps of high electrical and thermal conductance. On the other hand, uncooled temperature sensitive detectors need solder bumps with high electrical conductance but minimal thermal conductance.
The most recent prior art in staring system technology uses metal bumps which provide the needed high electrical and thermal conductance for cooled detectors but which cause excessive thermal conductance for uncooled detectors. Unfortunately, cooling in infrared detector systems requires expensive complex cryogenic coolers to maintain the detectors at proper operating temperatures. Such systems tend to be bulky, weighty and not readily susceptible to mass production techniques. Furthermore, they tend to have a lifetime which is limited by the life of the cooling system. However, the aforementioned thermal conductance problem stemming from the use of metal bumps in staring systems, results in a significant disadvantage to the use of uncooled, two-dimensional temperature sensitive detector arrays. More specifically, current arrays of the uncooled configuration operate about two orders of magnitude below the performance capabilities of ideal uncooled detectors because the excessive thermal conductance of metal bumps reduces the signal and increases the temperature fluctuation noise generated by the heat flow between the detectors and the environment.
The present invention decreases thermal conductance by reducing the cross-section and increasing the length of the support link between the detector and its environment. In addition, materials of minimal thermal conductivity are used for the detector support and detector leads having minimum heat conductance are employed. These thermal conductance reducing features are provided within the constraints of a two-dimensional detector array with negligible dead space in the focal plane, that is, space which does not respond to the infrared signal. The present invention thus reduces the performance diminishing thermal conductance significantly and yet does so in a two-dimensional detector array in which more than 90% of the array area converts the incident infrared radiation into electrical signals. It does so by combining a unique foacl plane with three principal features, a two-dimensional array of radiation concentrators, a detector support structure for two-dimensional array of widely separated uncooled detectors and an integrated circuit substrate for reading out the signals of the detector array.
The following issued U.S. patents are deemed to be pertinent to the present invention but without affecting its patentability.
U.S. Pat. No. 3,639,765 to Kleinerman is directed to an infrared image converter utilizing collecting optics such as a parabolic mirror to collect an infrared image and focus the image onto a screen.
U.S. Pat. No. 4,079,507 to King discloses silicon insulator polysilicon infrared imaging devices with edge detectors. The detectors have a trapezoid cross-section with perforations of the mask at one end.
U.S. Pat. No. 3,845,296 to Schnitzler is directed to a photosensitive junction controlled electron emitter and provides for a sandwich structure of photosensitive junctions in series with the mosaic of photo emitters.
U.S. Pat. Nos. 4,080,532; 4,162,402; and 4,379,232 to Hopper are directed to a ferro electric imaging system, and represent the current state of the art in two-dimensional solid state, uncooled thermal imaging.
U.S. Pat. No. 3,746,454 to Pace et al is directed to an infrared receiver for optical radar and discloses a plurality of microlenses, each of which utilizes a respective detector element but not for thermal isolation.
The patents to Chapman and Chapman et al, U.S. Pat. Nos. 4,029,962 and 3,989,946, respectively, discloses a pair of infrared image detection arrays which have certain pertinent geometric characteristics.